Today, tampon applicators represent a common means used by women to position a catamenial tampon into their vaginas. Many such applicators consist of two hollow, cylindrical tubes telescopically attached together. Such tampon applicators include an outer tube which contains a tampon and an inner tube which is used to expel the tampon from the outer tube. The applicator can be constructed of various materials including paper, cardboard, coated paper or plastic.
Up until now, the outer tubes of such tampon applicators have been manufactured having a straight cylindrical axis. This is especially true for outer tubes which are injection molded from synthetic or thermoplastic resins. One reason for this is that it is extremely difficult to engineer, design and build a mold that can produce an arcuately-shaped article having a hollow interior. Such molds are also very expensive to build and maintain. It is a challenge to design a mold which is capable of inserting and withdrawing an inner core into and out of an arcuately-shaped cavity without destroying the molded article. One approach is to construct a mold using a multitude of movable parts. However, the fit between two adjacent parts creates an area into which molten material can flow. When the surfaces of the two adjacent parts are not machined to a close tolerance, molten material can flow into such areas and create flash lines on the exterior surface of the finished article. Such flash lines are unacceptable and the article has to be discarded.
Another problem with injection molding arcuately-shaped hollow articles is that it is extremely difficult to mold such articles at high speeds needed for commercial operations. Unlike an extrusion molding process, injection molding is a batch operation which is dependent upon cycle time. A complete cycle includes closing the mold, introducing molten material, cooling the material so that it solidifies to form an article, opening the mold and then removing the finished article. As the cycle time increases, the number of articles which can be molded per minute decreases. One is also limited by the size of the mold. Large molds having more than 64 cavities are difficult to build and operate. Such large molds also require an injection molding machine that can deliver extremely high closing pressures and require complex controls for maintaining an even distribution of temperature across the entire surface of the mold. If a mold is operated with temperature variations between the cavities, certain cavities will not be capable of forming a complete article and this will result in increased waste. Because of the above-identified problems, no one has introduced an arcuately-shaped tampon applicator into the market place which has been injection molded.
Now a process has been invented for injection molding arcuately-shaped hollow articles at commercial speeds in an efficient manner and at a relatively low cost.